Experimental Study On Permeability Of Concrete Under Cyclic Loadings

Resistant to penetration of concrete is not enough which is the chief cause of the durability problem,the micro-cracks which caused by heat of concrete hydration has minimal impact on penetration of concrete,but when the concrete is subjected to loads,the new cracks will be formed based on the initial cracks inside the concrete,and these new cracks will keep propagating as the load and loading cycles increasing,which decreases the resistant to penetration of concrete rapidly and influences the durability of concrete.The researcher usually ignore the effect of the load to just research the penetration of intact concrete and use the load level as parameter in the research, which causes the results of the experiment lacks applicability and does not agree with the reality.Based on this question,in this article the water absorption and chloride diffusivity of C30and C60concrete specimens which has been applied different cyclic load and loading cycles are researched,and the effects of load on permeability is analyzed by experimental results.Besides,the relationship between water absorption,chloride diffusivity of concrete which has applied cyclic load and the damage variable defined by ultrasonic velocity,residual strain is researched according to the result of measurement.The contents and conclusion of this article as following:(1) On the basis of existing research,the author has made experiments on water absorption and chloride diffusivity of two different concretes which has applied different cyclic load and loading cycles,and obtained the water absorbing coefficient,chloride ion diffusion coefficient and surface chloride ion concentration by curve fitting and theoretical calculation,it can be found that these parameters will increase as the load and loading cycles increasing,and there is a critical load level which is about0.6,if load level over the critical load level,the growth rate of these parameters will increase rapidly.(2) The water absorbing coefficient is correlated with chloride ion diffusion coefficient for the same concrete,and they are accord with second order curve approximately.(3) According to the analysis of the ultrasonic velocity and residual strain,it found that the damage variable and residual strain will increase as the load level and loading cycles increasing,and damage variable has a favorite relativity with residual strain.(4) From the fitting curves of A-Dv,D-Dv,A-εr and D-εr,the relation between chloride ion diffusion coefficient,water absorbing coefficient and damage variable,residual strain accords with exponential function approximately,which is further proved that damage variable and residual strain can be put as the study parameters to research the penetration of damaged concrete.